Modbus - Problem when read data from Schneider PM1200 by Arduino MEGA 2560

I am writing a Modbus program to get data from Schneider PM1200 by Arduino MEGA 2560. Arduino is Master, device is slave.
However, program always notify error "Time out". I can't get data from register of device.

1. Mission:
Read data from registers of Schneider PM1200 by Arduino ( Modbus Master)

Link : http://www2.schneider-electric.com/...S/212000/FA212509/en_US/PM1000_User_Guide.pdf (page 53)

2. Connection Diagram

Devices include:
Arduino Mega 2560
Module RS485 - MAX485
PM1200

3. Library and code:
I use Modbus Master library.

Link library: https://github.com/smarmengol/Modbus-Master-Slave-for-Arduino

Code read data from register 3927: https://codebender.cc/sketch:708363

4. Problem
When I run code in IDE Arduino, monitor display error 226 - Time out
I tried to use Arduino Nano, the monitor still displayed that error.

Then I remove Arduino and just use RS485.
- When I use Modscan software. I can completely read data from device

- When I use QModMaster software. I can not read data and program notify error Time out.Program sent exactly request but there is nothing returning.

Is there something wrong with the request signal? Am I making any mistakes in the circuit or the code?

Please contact me by email : [email protected]
Any pointers would be greatly appreciated.